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This lesson introduces random sampling, one of the key concepts employed by scientists to study the natural environment, including microbial communities. Students first learn about the abundance and diversity of marine microbes. Colored beads in a bag are then used to represent different types of microbes, with the bag itself representing the ocean. Working in groups, each student randomly samples ten "microbes" from the "ocean", and records the data. To learn about the inherent variability of random sampling, the students then compare the composition of their individual samples, their group’s pooled sample data, and that of the entire population.

Intended Audience

5-8 X 
9-12 X
Learning Objectives


At the completion of this activity, the learner will:

    1. Gain an appreciation of the vast abundance and diversity of marine microbes.
    2. Understand how and why scientists obtain random samples.
    3. Understand that large samples tend to more closely approximate population parameters.

Necessary Student Background

This activity requires that students be comfortable with arithmetic, including the calculation of percentages.


Diversity, statistics, counting, microbial abundance

Print a PDF of this activity

Quantifying Marine Microbes: A Simulation to Introduce Random Sampling (19 pages)